Exoplanet spin measured for first time

Eight-hour day on Beta Pictoris b is shorter than day of any planet in our solar system

AS THE WORLD TURNS On Beta Pictoris b (upper right, in an artist’s illustration), a day is just over eight hours long. The exoplanet spins almost twice as fast as Jupiter does (when measured at the equator). The exoplanet’s spin continues a trend seen in our solar system: More massive planets spin faster.

Astronomers have measured the rotation of an exoplanet for the first time. A day on the planet Beta Pictoris b is roughly eight hours long — shorter than on any planet in our solar system, the researchers report in the May 1 Nature.

Beta Pictoris b orbits a young star 63 light-years away in the constellation Pictor. To measure the planet’s rotation, Ignas Snellen, an astronomer at Leiden Observatory in the Netherlands, and colleagues analyzed the planet’s spectrum. The spectrum reveals certain wavelengths of light that are absorbed by carbon monoxide in the planet’s atmosphere. By measuring how much the absorbed wavelengths are Doppler shifted by the rotating atmosphere, the researchers determined how quickly the planet spins.

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